In one aspect, this invention relates to an improved processing technology for additive blends in a polymer resin carrier, including those which are highly loaded with additives, using solid state compaction processing using a tubular die.
The technology of producing masterbatches of additives in polymers has been practiced in the polymer industry for many years. In an improved version of this art, a high percentage of additives can be incorporated in the masterbatch. These blends have been described as Type A Superblends by Ingenia Polymers Inc. (Houston, Tex.). Here, the additive loading typically is in the range of 50 to 90% by weight. Such highly loaded masterbatch preparation practice is taught by S D'uva et al, in US Patent Publication No. 2008/0076857A1 (2008), the entire content of which is hereby incorporated by reference. During its processing the polymer resin carrier (10-50%) is melted, for example in a twin screw extruder. While the processing method of Type A Superblend is generally applicable to many additives, a major limitation of this technology, as has been discovered, is that for some low-melting, sticky additives, pelletization cannot be achieved by the traditional melt extrusion technology.
Compaction technology to prepare pellets of additive blends is known to those skilled in the art, e.g. A. M. Chatterjee et al, European Patent 2,373,730, issued May 8, 2013; and US Patent Publication No. US2010/0152341A1 (2010), the entire contents of both of these, namely the European patent and U.S. patent application, being hereby incorporated by reference. These patents teach a process for improving the compacted pellets' resistance to friability or attrition. This process is directed to 100% additive blends containing no polymer resin carrier.
U.S. Pat. No. 6,515,052 (Albemarle Corporation, Baton Rouge, La.), entitled “Granular Polymer Additives and Their Preparation,” describes using a solvent in a compaction process to improve the yield and quality (lower friability) of a compacted additive blend including a phosphite stabilizer. A solvent (e.g. cyclohexane) is added to the dry additive blend and subsequently the mixture is processed through a pellet mill. The solvent partially solvates the phosphite stabilizer. After passing through the pellet mill, the solvent is removed. No polymer resin carrier is present.
U.S. Pat. No. 6,800,228 (Albemarle) entitled “Sterically Hindered Phenol Antioxidant Granules Having Balanced Hardness” describes using a solvent for the preparation of compacted additive blends including a phenolic antioxidant. This patent extends the technology taught in U.S. Pat. No. 6,515,052 to phenolic antioxidants. The solvent is usually alcohol, cyclohexane or a mixture thereof; adjusting the amount and ratio of the solvents can control the hardness and friability of the pellets produced. No polymer resin carrier is present.
U.S. Pat. No. 6,596,198 (Albemarle) teaches compacted pellet blends, where the stabilizer additive system comprises at least a stabilizer and a processing aid, preferably a mold release agent. The stabilizer comprises less than 50% of the combined total weight of the stabilizer and the mold release agent. No polymer resin carrier is present.
U.S. Pat. No. 6,033,600 (General Electric Company, Fairfield, Conn.) describes compacted pellet blends, typically a mixture of 10-90% penta-erythritol diphosphite, 10-90% phenolic antioxidant, 2-60% metallic stearate and 1-10% hydrotalcite. No polymer resin carrier is present.
U.S. Pat. No. 5,773,503 (1998) by W. P. Steen describes compacted pellet containing mineral filler and method for making the same. Additive blends containing talc and binder like erucamide were compacted to produce pellets. No polymer resin carrier is present.
U.S. Pat. No. 5,846,656 (Ciba Specialty Chemicals, Basel, Switzerland) covers a pellet mill type compaction process where 2-50% of a ‘melt preventing compound’ (binding agent) is added to a stabilizer or additive system to prevent melting of the stabilizer. The binder can be hindered phenolic antioxidant (AO) like Irganox® 1076 (BASF), glyceryl mono-stearate (GMS), oleamide, etc. Any polymer component, if present, was specified to be of less than 100 micrometer (micron) median particle size.
These references provide for low-dusting forms of additive blend pellets which can be more conveniently and accurately fed to post-reactor extrusion operations for addition to a polymer in a polymer resin producing plant. Such solid additive blend pellets are added directly to a polymer stream into an extruder or other melt processing device, whereby the polymer is melted and the additives are blended into the molten polymer, which is subsequently pelletized, thus producing polymer resin pellets containing desired concentration of additives.
What is needed, therefore, is a method for processing pellet blends of high concentrations of low melting, sticky additives, including a polymer resin carrier, which blends cannot be processed into pellets successfully by traditional melt extrusion processes. The low melting sticky additives have other attractive properties, e.g. as an antistatic agent or antioxidant for polymers.